The concentration of ions, such as potassium, sodium, chloride, and calcium, in the extracellular fluid (ECF) of a patient is of clinical significance. Abnormal ion concentration levels in the ECF can be a product of the pharmacological management of patients with heart failure. In general, the concentration of potassium and calcium ions in the intracellular fluid (ICF) of cardiac muscle or other tissue is high in comparison to potassium and calcium ions in the ECF. In contrast, the concentration of chloride and sodium ions is greater in the ICF than the ECF. As an example, elevated potassium ion concentration, denoted [K+], in the ECF causes a reduced concentration gradient between ICF and ECF. A reduction of the resting membrane potential is associated with the reduction in the concentration gradient, often resulting in ectopic foci and arrhythmia.
A reduction in concentration gradient further affects the magnitude and duration of the action potential. The change in membrane potential caused by an action potential, which is about 120 mV in healthy cardiac muscle, can be reduced substantially. In addition, the duration of the action potential, which is about 250 milliseconds in healthy cardiac tissue, can be diminished.
The concentration of ions may have additional clinical significance as well, and for some patients the certain ion concentrations may be an important factor worth monitoring. For example, trauma patients, burn patients, diabetic patients with ketoacidosis, renal patients on dialysis, patients experiencing pulmonary edema, and cardiac arrest patients may have electrolyte fluctuations, particularly fluctuations of potassium ion concentrations. In addition, potassium ion retention accompanies the onset of some medical conditions, such as Addison's disease.